This invention relates to hydraulic force multiplying devices for use in apparatus such as hydraulic braking systems of vehicles or the like.
Various hydraulic force multiplying devices have been proposed to generate an augmented output force by utilizing hydraulic pressure. One of the prior art hydraulic force multiplying devices includes a housing having an inlet port connected to a source of hydraulic pressure and an outlet port, an input rod and an output rod the one ends of which are slidably connected with one another within the housing, a free piston slidably disposed between the outer circumference of the input rod and the inner wall of the housing and dividing the interior of the housing into an inlet side oil chamber and an outlet side oil chamber and being associated with the output rod, a passage formed in the input rod for connecting the two oil chambers, and a valve for controlling oil flow in the passage. The valve consists of a rigid valve member secured to the input rod and a valve seat formed on the output rod so that the effective passage area is throttled when the two rods approach one another. When an input force is applied to the input rod to move it into the housing the valve member on the input rod approaches the valve seat thereby reducing the passage area. A differential pressure is generated across the free piston, and a differential pressure force acting on the free piston is transmitted to the output rod.
The hydraulic force multiplying device having such a construction aforementioned operates satisfactorily in normal operating conditions. However, when the input rod is moved rapidly toward the output rod such as in emergency conditions or the like, the pressure in the inlet side oil chamber may so rapidly that the valve member engages impactively with the valve seat, and there are shortcomings such that the valve will sometimes be damaged and, further, since the force applied to the input rod is transmitted directly to the output rod, the driver of the vehicle will feel that the brake pedal is blocked.
Further, the hydraulic force multiplying device may sometimes be incorporated in a hydraulic system such that the device and one or more separate hydraulic actuating devices such as a power steering device or the like are arranged in series in the system. In such case, when the valve member engages with the valve seat, the oil flow through the outlet port will be reduced excessively or to zero, whereby the function of separate hydraulic actuating devices will be lost.